The overall aim of the proposed research is the elucidation of the molecular mechanisms underlying the regulation of the brain opiod systems. Mu, delta and K opioid receptors mediate the actions of opioid drugs and the three classes of opioid peptides, beta- endorphin, the enkephalins and dynorphin-related peptides, upon nervous tissue. Experiments are designed to examine 1) the regulation of opioid receptors and peptides in adult brain by exogenously adminisstered opioids and 2) the regulation of the expression of opioid receptors and peptides in development. this laboratory has demonstrated that chronic antagonist treatment produces a coordinated upregulation of mu and delta receptors and an increase in enkephalin levels in several brain regions. Long- term exposrue of cells to delta opioids is known to produce receptor downregulation in vitro, but not in vivo. This research proposal aims to extend these phenomenological observations to a molecular mechanistic level. A combination of receptor readioautographyc and molecular biological techniques will be used to elucidate the molecular event s underlying opioid receptor and peptide regulation in vivo. Specifically, the following questions will be addressed: 1) Do exogenous opioids alter opioid receptor and peptide synthesis rates? 2) Does this occur at the transcriptional or translational levels? 3) Are opioid peptides and receptors regulated differnetially throughout the brain? the second section of the proposal aims to identify factors which influence opioid receptor and peptide expression in development. Primary cultures of striatal and hypothalamic neurons will be used as model systems to study the effects of neuronotrophic factors, innervation, cell-cell contact and target organ interactions upon opioid receptor and peptide expression. Together, these studies are expected to provide important new information about the regulation of this major transmitter-receptor system of the central nervous system and to elucidate mechanisms underlying opioid tolerance and dependence.